Web documents have many of the same elements as print documents but there are some points you need to remember. Web documents:
- frequently move or are removed from a site.
- often do not have: page numbers, publication dates, or authors, etc.
So, it is important to state whatever information you have in your reference list and citation.
New points in APA 6th Ed., are that you do not have to include:
- retrieval dates unless the source material may change over time (e.g., wikis).
- database information unless the item is an archival document (e.g., discontinued journal, monograph, or dissertation that was not formally published somewhere else).
(American Psychological Association, 2010, p. 192 )